Study the optical properties of XC (X = Si, Ge and Sn) nanosheets using TB-mBJ exchange-correlation potential

In this work, dielectric function, energy loss function, absorption, refraction index and reflectivity of graphene-like nanosheets of Si-C, Ge-C and Sn-C are calculated in the presence of a polarized electric field parallel (E parallel to x) and perpendicular (E parallel to z) to the surface of the hexagonal nanosheets. Our calculations are based on the density functional theory (DFT) with full potential linearized augmented plane-waves (FP-LAPW) basis. Generalized gradient approximation (GGA) and the Tran & Blaha modified Becke-Johnson (TB-mBJ) potentials are used for exchange-correlation potential. The results show that the optical properties of all the nanosheets are extremely polarization-dependent and have a significant anisotropic behavior especially in the visible region of the electromagnetic waves. Furthermore, the calculated value of static dielectric constant by TB-mBJ is less than GGA and also it is increased as we go down the periodic table from Si to Sn in our nanosheets. Also, our findings by the two methods demonstrate that for the E parallel to z polarization, the refraction index is nearly constant in the visible region for all the three nanosheets, which shows the promising applications of these nanosheets in optical fiber devices. Finally, since the band gaps obtained by TB-mBJ method are very close to the experimental band gap, the optical properties obtained by TB-mBJ potential of this work may be used for the future optoelectronic applications of these nanosheets.